Blade control system for bulldozer

ABSTRACT

A blade control system for a bulldozer enables the bulldozer to effectively perform a ground leveling work or a grading work with high accuracy in a minimum amount of time. The system compensates for pitching of a tractor portion of the bulldozer, and for variations in the amount of earth to be moved by a blade of the bulldozer. The system comprises: a pair of photo receivers (2, 3) which are mounted on the tractor portion (1) along a longitudinal axis of the portion (1) while spaced apart from each other, each of which receivers (2, 3) detects an optical reference plane (6) produced by a photo projector (4) to issue a level signal; and a blade controller (13) which controls an hydraulic valve actuaor (14) for moving the blade (8) based on the level signals. The receivers (2, 3) can detect a three-dimensional position of the tractor portion (1), and the blade controler (13) controls the actuator (14) upon receipt of an output signal issued from a position-measuring controller (23) which receives the level signals issued from the receivers (2, 3) to calculate a progress of the work.

FIELD OF THE INVENTION

The present invention relates to a blade control system for a bulldozer,and more particularly to blade control system of a bulldozer forperforming ground leveling work or a grading work based on signalsissued from a level detecting unit, such as a photo receiver, mounted ona bulldozer, the level detecting unit being adapted to detect an opticalreference plane which is formed by an optical projector so as to behorizontal in a predetermined range of area or so as to be inclined atan arbitrary angle in the area.

In addition, the present invention relates to such blade control systemfor the bulldozer, in which system the level detecting unit, e.g., aphoto receiver, has the facility for detecting a three-dimensionalposition of the bulldozer so as to make it possible that an operator ofthe bulldozer measures progress of the ground leveling work or of thegrading work.

BACKGROUND OF THE INVENTION

In ground leveling work or grading work performed over a wide range ofarea, a bulldozer is generally used. In this case, the more the range ofarea increases, the more the leveling control in ground finishing workor in grading work is important. Consequently, heretofore, it is usualto perform the ground finishing work with reference to a reference planewhich is measured each time the ground finishing work is performed afterthe bulldozer performs the primary ground leveling work (hereinafterreferred to as the "first conventional method").

On the other hand, in recent years, a second conventional method hasbeen also developed for performing the ground leveling work or thegrading work based on a reference plane which is formed by scanning awork area or ground with a laser beam light issued from a rotary laserprojector installed in the work area.

In the second conventional method, the rotary laser projector isrotatably driven to form a horizontal optical reference plane or anoblique optical reference plane inclined at an arbitrary angle. A photoreceiver for receiving a laser beam light issued from the laserprojector is mounted on a bulldozer, and serves as a ground-leveldetecting unit for detecting a level of the ground relative to theoptical reference plane to issue a level signal to a control unit of thebulldozer, so that a position of a blade of the bulldozer isautomatically controlled based on the level signal to perform groundleveling work or grading work in an appropriate manner.

However, the above first conventional method is tedious and timeconsuming, and is poor in finishing quality of the ground leveling work.

On the other hand, the second conventional method suffers from a problemin that, since the ground-level detecting unit is directly mounted onthe blade of the bulldozer so as to control a position of a cutting edgeof the blade serving as a level target in the ground leveling workduring which a tractor (which is a main vehicle body portion of thebulldozer) pitches considerably, a level signal or value issued fromsuch ground-level detecting unit extremely varies from that of theoptical reference plane during the ground leveling work. In addition, inthe second conventional method, the bulldozer is restricted in workingspeed when its work area includes large concave and convex groundportions. Further, in the second conventional method, when the laserbeam light issued from the rotary laser projector is interrupted by theother construction machines such as dump trucks, there is a fear thatthe position of the blade is not appropriately controlled since theposition of the blade is controlled based on the level signal havingbeen received before such interruption.

In addition, heretofore, in the ground leveling work or the grading workperformed over a wide area, since it is general for a constructionmanager to empirically divide the area and empirically decide theexecution order of the work in the area, the work is not necessarilyperformed in an effective manner.

SUMMARY OF THE INVENTION

In view of the above circumstances, the present invention was made.Therefore, it is an object of the present invention to provide a bladecontrol system for a bulldozer, which system enables an operator of thebulldozer to effectively perform ground leveling work or grading workwith high accuracy, regardless of the presence of pitching motion of atractor or main vehicle body portion of the bulldozer in the work.

It is another object of the present invention to provide a blade controlsystem for a bulldozer, which system enables an operator of thebulldozer to perform a uniform smoothing control of the finished groundsurface and of the graded ground layer with high accuracy in a minimumof time, regardless of the amount of the earth to be removed by theblade.

The above objects of the present invention are accomplished inaccordance with a first aspect of the present invention as follows.

In a blade control system for a bulldozer comprising, in order toperform ground leveling work or grading work by automaticallycontrolling a vertical position of a blade of a bulldozer during thework: a light projecting means for forming over a predetermined area ahorizontal optical reference plane or an oblique optical reference planeinclined at an arbitrary angle, the light projecting means beinginstalled in a place remote from the bulldozer; a light receiving meanswhich is mounted on a tractor body portion of the bulldozer, and detectsthe optical reference place formed by the light projecting means toissue a level signal; and a control means which receives the levelsignal to control a hydraulic valve actuator based on the level signal,which hydraulic valve actuator moves the blade of the bulldozer; theimprovement wherein,

the light receiving means comprises at least a pair of photo receiverswhich are arranged along a longitudinal axis of the tractor body portionof the bulldozer while spaced apart from each other, and a bladecontroller which controls the hydraulic valve actuator based on outputsignals issued from the pair of the photo receivers.

Further, the above objects of the present invention are accomplished inaccordance with a second aspect of the present invention, as follows:

The blade control system for the bulldozer as set forth in the firstaspect of the present invention, wherein:

the light projecting means comprises a pair of photo projectors;

each of the photo receivers of the light receiving means has thefacility for detecting a three-dimensional position of the tractor bodyportion of the bulldozer; and

the blade controller of the light receiving means controls the hydraulicvalve actuator based on an output signal issued from a positionmeasuring controller, which position measuring controller receives thelevel signal issued from each of the photo receivers to obtain progressdata of the work.

In addition, the above objects of the present invention are accomplishedin accordance with a third aspect of the present invention, as follows:

The blade control system for the bulldozer as set forth in the firstaspect of the present invention, wherein:

the blade control system further comprises a cylinder stroke sensorwhich detects a stroke of the hydraulic valve actuator to issue a strokesignal of the thus detected stroke, the stroke signal being fed back tothe blade control system.

Still further, the above objects of the present invention areaccomplished in accordance with a fourth aspect of the presentinvention, as follows:

The blade control system for the bulldozer as set forth in the secondaspect of the present invention, wherein:

further mounted on the bulldozer in addition to the photo receivers area wireless unit and an on-vehicle monitor; and

further installed on the ground are a ground wireless unit and a groundmonitor.

In the present invention having the above aspects, when a ground leveldetecting unit (e.g. photo receivers) detects an optical reference planeformed by the photo projectors to issue a level signal, the bladecontroller determines an angle at which a frame of the blade is inclinedbased on a value of the level signal so as to automatically change astroke of a cylinder which moves the blade. Consequently, in the presentinvention, it is possible for an operator of the bulldozer to smoothlyperform predetermined ground leveling work regardless of the presence ofpitching of a tractor body portion of the bulldozer. In addition, sinceat least a pair of the photo receivers are mounted on the bulldozer soas to be spaced apart from each other along a longitudinal axis of thetractor body portion of the bulldozer, it is possible for the operatorto control the bulldozer with high accuracy in the work.

Further, in the present invention, since the ground level detecting unit(e.g. photo receivers) having the facility for detecting athree-dimensional position of the tractor body portion of the bulldozeris mounted on the tractor body portion so that the photo receivers arespaced apart from each other along the longitudinal axis of the tractorbody portion of the bulldozer to make it possible to automaticallycontrol the progress of the work in a predetermined manner, thebulldozer with the blade control system of the present invention isadvantageous in that, when the ground leveling work or the grading workis performed over a wide area, the blade control system of the presentinvention enables an operator of the bulldozer to perform a uniformsmoothing control of the finished ground surface and of the gradedground layer with high accuracy in a minimum of time, regardless of theamount of the earth to be removed by the blade.

The above objects, additional objects, additional embodiments, andadvantages of the present invention will be clarified to those skilledin the art hereinbelow with reference to the following description andaccompanying drawings illustrating preferred embodiments of the presentinvention according to principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic side view of a first embodiment of theblade control system of the present invention, illustrating the entireconstruction of the embodiment;

FIG. 2 is a block diagram of the blade control system of the presentinvention shown in FIG. 1;

FIG. 3 is a flowchart of a process of controlling the blade of thebulldozer performed by the first embodiment of the present inventionshown in FIG. 1;

FIG. 4 is an overall schematic perspective view of a second embodimentof the blade control system of the present invention, illustrating theentire construction of the embodiment;

FIG. 5 is an x-y coordinate system for showing, in plan view, a positionof each of the light projecting means and the light receiving meansemployed in the second embodiment of the present invention;

FIG. 6 is a schematic perspective view of the light receiving meansemployed in the second embodiment of the present invention shown in FIG.4, illustrating the construction of the light receiving means;

FIG. 7A is a side view of the bulldozer, employed in calculation of theprogress of the work performed with the use of the second embodiment ofthe present invention shown in FIG. 4;

FIG. 7B is a geometrical side view of essential parts of the bulldozer,employed in calculation of the progress of the work performed with theuse of the second embodiment of the present invention shown in FIG. 4;

FIG. 8 is a diagram illustrating a method for storing necessary data ofthe progress of the work performed by the second embodiment of thepresent invention shown in FIG. 4;

FIG. 9 is a diagram illustrating a method for displaying the necessarydata of the progress of the work performed by the second embodiment ofthe present invention shown in FIG. 4;

FIG. 10 is an overall schematic diagram of the second embodiment of theblade control system of the present invention shown in FIG. 4;

FIG. 11 is a contour map for illustrating the progress of the workaccomplished by the second embodiment of the present invention shown inFIG. 4; and

FIGS. 12 and 13 are cross-sectional views of the contour map, takenalong the line A-A'.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, two preferred embodiments of a blade control system for abulldozer of the present invention will be described in detail withreference to the accompanying drawings.

First, with reference to FIGS. 1 to 3, a first embodiment of the presentinvention will be described.

Now, as shown in FIG. 1, in the first embodiment of the blade controlsystem for the bulldozer, a pair of light receiving means or photoreceivers 2 and 3, each of which detects a laser beam light to determinea position of the bulldozer, are mounted on a front portion A and a rearportion B of a tractor body portion 1 of the bulldozer, respectively. Onthe other hand, a light projecting means or photo projector 4 is mountedon a stand 5 disposed in a place remote from the bulldozer. The photoprojector 4 is of a rotary type adapted to issue a laser beam light inany desired direction, and may from a horizontal optical reference plane6 over a predetermined area in which ground leveling work or gradingwork is performed. In addition, in case that the ground leveling work orthe grading work must be performed parallel to an oblique ground surfacein the area, the photo projector 4 may issue a laser beam light to forman oblique optical reference plane inclined at the same angle as that ofthe oblique ground surface. Now, the ground leveling work performed withreference to the horizontal optical reference plane 6 formed by thephoto projector 4 will be described.

In operation, the laser beam light issued from the photo projector 4 andforming the optical reference plane 6 is detected by the pair of thephoto receivers 2, 3 mounted on the tractor body portion 1 of thebulldozer. In the first embodiment of the present invention, as shown inFIG. 1: a tractor reference plane 7 is formed between the photoreceivers 2, 3 on the tractor body portion 1 of the bulldozer, whereinthe tractor reference plane 7 is parallel to a longitudinal axis of thetractor body portion 1 of the bulldozer; the reference character h_(F)denotes a distance between the tractor reference plane 7 and a lightreceiving point C of the photo receiver 2, at which point C the laserbeam light issued from the photo projector 4 is received by the photoreceiver 2; the reference character h_(R) denotes a distance between thetractor reference plane 7 and a light receiving point D of the photoreceiver 3, at which point D the laser beam light issued from the photoprojector 4 is received by the photo receiver 3; and the referencecharacter l₁ denotes a distance between the photo receivers 2 and 3. Inthis case, therefore, the angle of the tractor reference plane 7 of thetractor body portion 1 of the bulldozer from the optical reference plane6 is denoted by the reference character θ which is represented by thefollowing equation:

    θ=tan.sup.-1 ((h.sub.F -h.sub.R)/(l.sub.1))          (1)

Now, the ground leveling work will be described in detail. In FIG. 1:the reference character l₂ denotes a length of a frame 9 through which ablade 8 is connected with a central portion or point 0 of the tractorbody portion 1 of the bulldozer; the reference numeral 10 denotes ahorizontal target ground level to be accomplished by the blade 8; thereference numeral 11 denotes a tractor-bearing ground surface bearingthe tractor body portion 1 of the bulldozer; the reference character 0'denotes a point at which the tractor-bearing ground surface 11intersects with a line passing through the central point 0 of thetractor body portion 1 of the bulldozer, which line is perpendicular tothe ground surface 11; the reference character N denotes a central pointof the blade 8, at which central point N the blade 8 is connected withthe frame 9; the reference character h denotes a distance between thepoint 0' and the horizontal target ground level 10 which is parallel tothe optical reference plane 6; the reference numeral 6' denotes aphantom optical reference plane passing through the central point 0 ofthe tractor body portion 1 of the bulldozer, the phantom opticalreference plane 6' being parallel to the optical reference plane 6; andthe reference character M denotes a point at which the phantom opticalreference plane 6' intersects with the blade 8 in a condition in whichthe frame 9 is parallel to the tractor-bearing ground surface 11.

In the ground leveling work, as shown in FIG. 1, the blade 8 of thebulldozer is lowered by the cylinder 12 to remove earth to such anextent that the blade 8 reaches its phantom position 8' adjacent to thetarget ground level 10, in which phantom position 8' the blade 8 isconnected with the frame 9 at an intersection point N'. Consequently, avertical distance h between the point 0' and the target ground level 10is identical with a vertical distance between the point M of the blade 8and a horizontal plane passing through the point N' of the phantomposition 8' of the blade 8. This vertical distance h may be calculatedin a proper manner based on: the above data h_(F), h_(R), θ; a distanceH between the optical reference plane 6 and the target ground level 10;and a distance h_(c) between the tractor reference plane 7 and thetractor-bearing ground surface 11.

In the ground leveling work, as shown in FIG. 1, the angle θ at whichthe tractor body portion 1 of the bulldozer is inclined in pitchingmotion thereof relative to the horizontal optical reference plane 6 maybe represented by the following equation, because the angle θ is formedbetween the phantom optical reference plane 6' and a longitudinal axisof the frame 9:

    Δh=h-l.sub.2 ×sineθ                      (2)

wherein: Δh denotes a vertical distance between the point N of the blade8 and a horizontal plane passing through the point N' of the phantomposition 8' of the blade 8.

Consequently, in the ground leveling work, the cylinder 12 of thebulldozer is operated to tilt the frame 9 by an angle φ, so that theblade 8 is lowered by a distance Δh to make it possible to lower thecutting edge of the blade 8 to the target ground level 10.

Now, with reference to FIG. 2, the above operation of the cylinder 12 ofthe bulldozer will be described.

After the pair of the photo receivers 2, 3 receive the laser beam lightissued from the photo projector 4 to issue output signals to a bladecontroller 13, then, the controller 13 performs necessary calculationsbased on the output signals by the use of the above equations (1), (2)to issue an instruction signal (which has a value of, for example Δh) toa hydraulic valve actuator 14 which in turn operates the cylinder 12 ofthe bulldozer to tilt the frame 9 by the angle φ so that the blade 8 islowered by the distance Δh to reach the phantom position 8' thereof. Inthis case, a cylinder-stroke sensor 15, which is incorporated in thecylinder 12, measures an amount of stroke of the cylinder 12 and issuesa stroke signal fed back to the blade controller 13 to enable the blade8 to reach its phantom position 8' adjacent to the target ground level10. An example of the above process performed by the blade controlsystem of the present invention is shown in a flowchart seen in FIG. 3.In the ground leveling work, the above process is repeated by the bladecontrol system for the bulldozer of the present invention over the areato be leveled.

Now, a second embodiment of the blade control system of the presentinvention will be described with reference to FIGS. 4 to 13. Through thefirst and the second embodiment of the present invention, like referencenumerals apply to similar parts. Consequently, such similar parts of thesecond embodiment of the present invention will not be described toavoid redundancy in in description.

In FIG. 4 illustrates an overall schematic perspective view of thesecond embodiment of the blade control system for the bulldozer of thepresent invention, the reference character G denotes a ground station,and the reference character W denotes the bulldozer.

First of all, a pair of photo projectors 4₁ and 4₂, which are spacedapart from each other by a distance L, are installed on the groundstation G. In a substantially central position between the pair of thephoto projectors 4₁, 4₂ is installed a reference-light receiver S fordetecting a reference direction.

On the other hand, a pair of photo receivers 20 and 30 are mounted on afront and a rear portion of the tractor body portion 1 of the bulldozer,respectively. In addition to the photo receivers 20, 30, further mountedon the tractor body portion 1 of the bulldozer are: a wireless unit 3;the blade controller 13; on-vehicle monitor 22; and position-measuringcontroller 23.

Incidentally, since the other parts of the bulldozer do not relate tothe present invention, they are not described herein. In operation, theblade 8 of the bulldozer is operated by the cylinder 12 in which thecylinder-stroke sensor (not shown) is incorporated. The cylinder 12 isoperated through the hydraulic valve actuator 14 which is controlled bythe instruction signal issued from the blade controller 13.

In the ground station G, there are installed, a wireless unit 24 forreceiving signals issued to/from the bulldozer, and a ground monitor 25.

With reference to the above construction of the second embodiment of theblade control system of the present invention, a process for determininga work position of the bulldozer, which position is represented bypositions of the pair of the photo receivers 20, 30 of the bulldozerrelative to the pair of the photo projectors 4₁, 4₂ installed in thearea to be leveled by the bulldozer, will be described.

In order to facilitate description of the present invention, as shown inFIG. 5, an x-y coordinate system is employed, in which coordinate systema position of the photo projector 4₁ constitutes an origin of thecoordinate system, so that a position or point of each of the otherphoto projector 4₂, reference-light receiver S, and the photo receivers20, 30 mounted on the tractor body portion 1 of the bulldozer isrepresented by the abscissa and the ordinate of the point. FIG. 5 showsthe relationship between the positions of the photo projectors and thephoto receivers.

In operation, the photo projectors 4₁ and 4₂ are rotatably driven sothat the laser beam lights issued therefrom are swung from thereference-light receiver S to the photo receivers 20 and 30,respectively. Namely, the photo projector 4₁ is rotatably driven in acounterclockwise direction, while the other photo projector 4₂ isrotatably driven in a clockwise direction, as shown in FIG. 5.

In the above operation, an optical reference plane formed by the laserbeam light issued from the photo projector 4₁ is so formed as tocoincide in height and tilting angle with that formed by the laser beamlight issued from the other photo projector 4₂. Under suchcircumstances, the laser beam light issued from each of the photoprojectors 4₁, 4₂ is received by the reference-light receiver S eachtime each of the photo projectors 4₁, 4₂ completes one turn in apredetermined period of time Ta, Tb. Namely, in the period of time Ta,the photo projector 4₁ completes one turn, while the other photoprojector 4₂ completes one turn in the period of time Tb. The periods oftime Ta, Tb are measured by the ground monitor 25 (shown in FIG. 4)which transmits data of the thus measured periods of time Ta, Tb to thebulldozer W through the ground station G by the use of the wireless unit21, 24 (shown in FIG. 4), so that the data of the thus measured periodsof time Ta, Tb is stored in the position-measuring controller 23 (shownin FIG. 4).

In the above operation, further stored in the position-measuringcontroller 23 is data as to the distance L between the photo projectors4₁ and 4₂, an angle of Δα (Δalpha) formed between the x-axis and astraight line connecting the origin or photo projector 4₁ with thereference-light receiver S, and an angle Δβ (Δbeta) formed between thex-axis and a straight line connecting the other photo projector 4₂ withthe reference-light receiver S.

Further, in the operation, at a starting time when the reference-lightreceiver S receives each of the laser beam lights issued from the photoprojectors 4₁, 4₂, the position-measuring controller 23 starts tomeasure each of the periods of time ta₁, tb₁, ta₂, tb₂ until each of thelaser beam lights is received by each of the photo receivers 20, 30. Theperiods of time ta₁, tb₁ are measured until each of the laser beamlights is received by the photo receiver 20, and the periods of timeta₂, tb₂ are measured until each of the laser beam lights is received bythe photo receiver 30. The above starting time is determined when theground monitor 25 (shown in FIG. 4) detects a detection time at whichthe reference-light receiver S receives each of the laser beam lights,data of which detection time is immediately transmitted to the bulldozerW through the wireless unit 24 to permit the position-measuringcontroller 23 to start measuring each of the periods of time ta₁, tb₁,ta₂, tb₂ which are stored in the controller 23.

Then, the position-measuring controller 23 calculates the followingequations 1 to 4 based on the above data as to: the periods of time (Ta,Tb, ta₁, tb₁, ta₂, tb₂), the angles (Δα, Δβ); and the distance L; so asto determine angles α₁, α₂, β₁, β₂ of the photo receivers 20, 30 (shownin FIG. 5) together with positions (X₂₀, Y₂₀) and (X₃₀, Y₃₀):

    α.sub.1 =2π.ta.sub.1 /Ta                          1

    β.sub.1 =2π.tb.sub.2 /Tb

    α.sub.2 =2π.ta.sub.2 /Ta                          2

    β.sub.2 =2π.tb1/Tb

    X.sub.20 =L.((cos(α.sub.1 +Δα) sin(β.sub.1 +Δβ))/((sin(α.sub.2 +β.sub.1 +Δα+Δβ))

    Y.sub.20 =L.((sin(α.sub.1 +Δα)sin(β.sub.1 +Δβ))/((sin(α.sub.1 +β.sub.1 +Δα+Δβ))                           3

    X.sub.30 =L.((cos(α.sub.2 +Δα)sin(β.sub.2 +Δβ))/((sin(α.sub.2 +β.sub.2 +Δα+Δβ))

    Y.sub.30 =L.((sin(α.sub.2 +Δα)sin(β.sub.2 +Δβ))/((sin(α.sub.2 +β.sub.2 +Δα+Δβ))                           4

Now, a process for determining the progress of the ground leveling workperformed by the bulldozer with the blade control system of the presentinvention will be described.

As shown in FIG. 6, in each of the photo receivers 20, 30, a pluralityof photo receiver elements 1, 2, 3, . . . n are arranged in a verticalrow. In operation, when the laser beam light (denoted by the arrow shownin FIG. 6) is issued to the photo receivers 20, 30, one of the photoreceiver elements of each of the receivers 20, 30 receives the laserbeam light so as to determine a height or vertical position of the laserbeam light, at which position the laser beam light is detected by eachof the photo receivers 20, 30.

Consequently, as shown in FIG. 7A, in the ground leveling work, in casethat the blade 8 of the tractor body portion 1 of the bulldozer pushesearth on the tractor-bearing ground 11 in a condition in which thebulldozer is inclined or pitched, since each of the photo receivers 20,30 has the above construction, the horizontal optical reference plane 6is detected by them 20, 30 as if it were an oblique plane inclined at anangle θ relative to the tractor reference plane 7 shown in FIG. 1.

In FIG. 7A, the reference numeral 0 denotes a vehicle center of thetractor body portion 1 of the bulldozer; Q₁ a front point in a vehicleplane passing through the vehicle center 0, which plane is parallel tothe tractor reference plane 7 shown in FIG. 1, the front photo receiver20 being mounted on the tractor body portion 1 of the bulldozer at thefront point Q₁ ; Q₂ a rear point in the vehicle plane, the rear photoreceiver 30 being mounted on the tractor body portion 1 of the bulldozerat the rear point Q₂ ; and 0' a ground intersection point at which thetractor-bearing ground 11 intersects a line passing through the vehiclecenter 0, the line being perpendicular to the tractor-bearing ground 11.

In addition, FIG. 7A may be converted into a geometrically simplifieddiagram such as FIG. 7B in which: the reference character Z₁ denotes adistance between the front point Q₁ and the front photo receiver 20; Z₂a distance between the rear point Q₂ and the rear photo receiver 30; andH' a minimum distance between the horizontal optical reference plane 6and the ground intersection point 0'.

Consequently, as is clear from FIG. 7B, the minimum distance H' and theposition of the vehicle center 0 in the coordinate system may becalculated according to the following equations 5 and 6, respectively.Incidentally, in FIG. 7B: the reference numeral 20' denotes a frontintersection point at which the optical reference plane 6 intersects aline passing through the front point Q₁, the line being perpendicular tothe optical reference plane 6; 30' a rear intersection point at whichthe optical reference plane 6 intersects a line passing through the rearpoint Q₂, the line being perpendicular to the optical reference plane 6;R a central intersection point at which a line segment Q₁ -Q₂ passingthrough the points Q₁ and Q₂ intersects a line passing through theground intersection point 0', the line being perpendicular to theoptical reference plane 6.

In calculation of the minimum distance H', as shown in FIG. 7B: thedistances Z₁ and Z₂ may be detected by the photo receivers 20 and 30,respectively; a line segment 0-Q₁ passing through the vehicle center 0and the point Q₁ is known; a line segments 0-Q₂ passing through thevehicle center 0 and the point Q₂ is known; a line segment 0-0' passingthrough the vehicle center 0 and the ground intersection point 0' isknown; and the angle θ is negligible. Consequently, as is clear fromFIG. 7B: a line segment 20-Q₁ passing through the points 20 and Q₁ issubstantially equal in length to a line segment 20'-Q₁ passing throughthe points 20' and Q₁, so that twice the line segment 20-Q₁ issubstantially equal in length to twice the line segment 20'-Q₁ ; a linesegment 30-Q₂ passing through the points 30 and Q₂ is substantiallyequal in length to a line segment 30'-Q₂ passing through the points 30'and Q₂, so that triple the line segment 30-Q₂ is substantially equal inlength to triple the line segment 30'-Q₂ ; and a line segment 0-0'passing through the vehicle center 0 and the ground intersection point 0is substantially equal in length to a line segment R-0' passing throughthe central intersection point R and the ground intersection point 0'.As a result, the minimum distance H' may be derived from the followingequation 5:

    H'=((Z.sub.1 +Z.sub.2)/Z)+(the length of the line segment 0-0')5

On the other hand, the position (X₀, Y₀) of the vehicle center 0 in thecoordinate system may be derived from the following equation 6:

Namely, since the vehicle center 0 is a center of the line segment Q₁-Q₂, the x-coordinate X₀ and the y-coordinate Y₀ of the vehicle center 0may be derived from the following equation 6:

    X.sub.0 =(X.sub.20 +X.sub.30)/2

    Y.sub.0 =(Y.sub.20 +Y.sub.30)/2                            6

According to the process described above, the position-measuringcontroller 23 of the blade control system for the bulldozer of thepresent invention may calculate: the position of the bulldozer relativeto the photo projectors 4₁ and 4₂ in the coordinate system; and anecessary data in the ground leveling work relative to the opticalreference plane 6. Based on the thus calculated data, a desired data (x,y, H') of the progress of the work in each section in the area to beleveled may be obtained.

Now, based on the above data (x, y, H') of the progress of the work, thefollowing control will be described. In case that the area to be leveledassumes a square shape, as shown in FIG. 8, the area is divided into aplurality of square sections in both of an x- and a y-direction, suchas: x1, x2, x3, . . . , xn; and y1, y2, y3, . . . , yn, respectively.The desired data (xi, yi, hij) of the progress of the work in eachsquare section is stored in memory means incorporated in theposition-measuring controller 23 (or in a separate memory means) to forma two-dimensional data array, wherein: each of the suffix i, j mayassume 1, 2, 3, . . . , n. As shown in FIG. 9, the thus formedtwo-dimensional data array may be converted into a variable-densitypattern image display by the position-measuring controller 23. In thethus converted image display, a dense pattern represents a rapidprogress of the work, while a nondense pattern represents a slowprogress of the work.

Incidentally, as shown in FIGS. 11 and 12, the two-dimensional dataarray may be converted into a contour map image display or across-sectional image display taken along any desired direction.

In case of the contour map image display shown in FIG. 11, the operatorof the bulldozer monitors the display during the ground leveling workand operates the bulldozer so that: a concave portion of the groundrelative to the target ground level, which portion is represented by adotted area, is filled with earth up to the target ground level; and inconvex portions of the ground relative to the target ground level (whichportions are represented by hatched areas), the bulldozer removes earthuntil it reaches the target ground level.

On the other hand, as is clear from the cross-sectional view shown inFIG. 12 of the area to be leveled, it is possible to easily calculatethrough integration the amount of earth to be filled in the concaveportion of the ground or to be removed from the convex portion of theground. Incidentally, as shown in FIG. 13, in the ground leveling work,the amount of earth to be filled in and removed from the portion of thearea may be adjustable in an appropriate manner.

Any of the above image displays may be monitored through the on-vehiclemonitor 22. In addition, the data of the progress of the work may betransmitted to the ground station G through the wireless units 21, 24 toenable the ground monitor 25 to store and display the data.

The block diagram of the blade control system of the present inventiondescribed above is shown in FIG. 10.

Transmission of the data between the ground station G and the bulldozershown in the block diagram of FIG. 10 is already described above indetail, and, therefore it is not described again. In the ground levelingwork, although the data of the progress of the work is obtained in theposition-measuring controller 23 as described above, in case that it isnecessary to move earth additionally, the position-measuring controller23 issues an earth-moving instruction signal to the blade controller 13.Upon receipt of the instruction signal, the blade controller 13 to makethe hydraulic valve actuator 14 (shown in FIG. 4) actuate the hydrauliccylinder 12, so that the cylinder 12 moves the blade 8 so as to performthe desired ground leveling work.

We claim:
 1. In a blade control system for a bulldozer for performingground leveling work or grading work by automatically controlling avertical position of a blade of a bulldozer during the work, of the typecomprising a light projecting means for forming over a predeterminedground area a horizontal optical reference plane or an oblique opticalreference plane inclined at an arbitrary angle, said light projectingmeans being installed at a location remote from said bulldozer; a lightreceiving means mounted on a tractor body portion of said bulldozer fordetecting said optical reference plane formed by said light projectingmeans to issue a level signal; and a control means which receives saidlevel signal to control a hydraulic valve actuator of said bulldozerbased on said level signal, which hydraulic valve actuator moves saidblade of said bulldozer, the improvement wherein:said light receivingmeans comprises at least a pair of photo receivers which arerespectively arranged along a longitudinal axis of said tractor bodyportion of said bulldozer and spaced apart from each other to form atractor reference plane therebetween; and a blade controller whichcontrols said hydraulic valve actuator based on a first output signalissued from one of said photo receivers at a first location on saidreference plane, and a second output signal issued from the other ofsaid photo receivers at a second location on said reference plane, saidsecond location being longitudinally spaced from said first location,said controller relating said tractor reference plane and said opticalreference plane.
 2. The blade control system for the bulldozer as setforth in claim 1, wherein:said light projecting means comprises a pairof photo projectors, each of said photo receivers of said lightreceiving means has the facility for detecting a three-dimensionalposition of said tractor body portion of said bulldozer; and said bladecontroller of said light receiving means controls said hydraulic valveactuator based on an output signal issued from a position measuringcontroller, which position measuring controller receives said outputsignal issued from each of said photo receivers to obtain progress dataof said work.
 3. The blade control system for the bulldozer as set forthin claim 2,further including a wireless unit and an on-vehicle monitormounted on said bulldozer in addition to said photo receivers; and aground wireless unit and a ground monitor installed on the ground. 4.The blade control system for the bulldozer as set forth in claim 1,wherein:said blade control system further comprises a cylinder strokesensor which detects a stroke of said hydraulic valve actuator to issuea stroke signal of the thus detected stroke, said stroke signal beingfed back to said blade control system.
 5. A blade control system for abulldozer, comprising:a bulldozer having a tractor body portion defininga longitudinal axis, a blade of said bulldozer for performing groundleveling work or grading work, means for controlling a vertical positionof the blade during the work, and means responsive to said controllingmeans for moving said blade in a vertical direction; light projectingmeans for forming over a predetermined ground area a horizontal opticalreference plane or an oblique optical reference plane inclined at anarbitrary angle, said light projecting means being located at a positionremote from said bulldozer and in light communication therewith; a lightreceiving means mounted on said tractor body portion of said bulldozerfor detecting said optical reference plane formed by said lightprojecting means to issue a level signal to said controlling means,whereby said controlling means controls said vertical position of saidblade in response thereto, said light receiving means comprising atleast a pair of photo receivers arranged along said longitudinal axis ofsaid tractor body portion of said bulldozer and spaced apart from eachother and forming a tractor body reference plane, said controlling meansbeing responsive in part to a distance between the tractor bodyreference plane and a tractor bearing ground surface to calculatevertical distance to be moved by said blade, said controlling meansbeing responsive in part to a first output signal issued from one ofsaid photo receivers at a first location on said reference plane, and asecond output signal issued from the other of said photo receivers at asecond location on said reference plane, said second location beinglongitudinally spaced from said first location, said controller.